Modulation system



April 23, 1929. c. A. cu LvER I MODULATION SYSTEM Filed July 16. 1926: I

' INVENTOR. f/zay' [05A a Z002;

ATTORNEY control the high frequency output of a radio any given instantthe potentials of the grids "20 vide a circuit arrangement at atransmitter thus existing in the inductances L and L Patented Apr. 23,1929. v

UNITED STATES PATENT OFFICE.

CHARLES A. CULVER, OF NQRTHFIELD, MINNESOTA, ASSIGNOR TO WIRED RADIO,INCL;

OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

MODULATION SYSTEM.

. Application filed July is, 1926. Serial N0.,122,986.

My invention relates broadly to circuits for to the antenna groundsystem 12 as shown controlling the output of a high frequency throughthe coupling inductance L electrical generator, and more particularlyHigh frequency energy from the master osto a system of modulation forusein con'ueccillator or driving circuit VT is tral'isferred 5 tion withradio telephone transmission or to the amplifier-modulator circuitthrough 5. broadcasting. the inductive relation obtaining between theOne of the objects of my invcntion'is to inductances L L and L The gridsof the effect an improvement in the means whereby 'triodes VT and VT arethus subjected to a voice generated potentials may be made to highfrequency alternating potential. At

t ans-nutter, and in particular to provide a of these tubes will differin, phase by 180. system whereby the necessity for se mrate Theresulting alternating current components modulating and amplifying tubesis climiinthe two plate circuits will, therefore, be nated. I y 2additive. However, the phase relation of 15 Another object of myinvention is'the supthe potentials on the grids due to certain har- 65pression'of hari'nonic frequencies in the high monies in the input willbe of such a nature frequency power circuit of a "radio transthat theresulting plate currents will nullify mitter. f one another, and thus besuppressed. The A further object of'my invention isto proen ergy of thepurified high frequencycurrent to secure greater over-all powerefliciency in transferred to the antenna ground system transmission. 1.i i through the inductive relation obtaining be- Still anotherobject ofmy invention is to tween L L and L In order to secure provide a systemof modulation for a t-ran higher power etficiency, the output circuit ofmitter wherebyfdistortion is reduced to a ,the amplifier-modulator tubesare adjusted f minimum. I, i to resonance with the frequency deliveredby f The invention will be more fully underthe driving circuit. This isaccomplished by stood by reference to the following specificameans ofthe capacitances C and C The tion and accompanying drawing which'showsinput circuit of these tubes may also be ad- 30- diagrammatieally awiring arrangement of justed to resonance with the driving circuit, 60 aradio transmitter embodying the principles though this is usuallyunnecessary and, in of my invention. fact, in most cases undesirable.The ampli- Referring to the drawing in detail the os tier-modulatororganization is less apt to oscillator tube VT together with theassocillate in and of itself if the grid circuits are ciated inductanceL capacitances C and C untuned. and the plate potential supply 135,constitute Modulation is. effected by means of the a master oscillatoror driving circuit. voice generated potentials developed in the Variousforms of oscillator circuits maybe secondary of thetransformer T, saidpotenemployed. 1 I tials being impressed 0n the grids of the tubes 10Thecomponent parts consisting of the in- VT and VT simultaneously withthe high ductances L L L, and L the capacitances frequency potentialsinduced by the master (I. 0 .0 and C the triode tubes VT, andoscillator. The. audio potentials developed the plate potential supply.B together at the terminals of the secondary of the transwith the usualfilament supply, constitute a former T will be opposite in sigmthat is.out 45 combinedbalanced amplifying and modul'atof phaseby 1809, andhence the grid of the ing system. tubes VT and VT will be subjected toon The transformer T, the microphoneM,(and posite audio potentials. As aresult of this battery B3 constitute the means whereby condition, theoperating point on one of said sound waves are causedto control ormodutubes will be moving upward on its character- 59 late theenergydelivered by the; organization istie. curve, whilethe operating pointon. the

ther tube will be moving downward. lhis condition will result in anincrease of output in one tube and a simultaneous decrease of output inthe other tube of the balanced pair, thus establishing a so-calledpuslrpull condition in theoutputcircuit of the tubes VT, and VT,. Theseaudio potentials cause the operating point of the grids of the tubes tomove up and down on their characteristic curves, and thus'the highfrequency output "or said tubes will be caused to vary in conformitywith the voice generated potentials. As a result, the amplidude of thehigh frequency current developed in the antenna. circuit will varyinaccordance with the audio frequency potentials impressed upon thegrids of the modulator-amplifier tubes, It will thus be seen thatmodulation iseftected without the use of separate modulating tubes, thusreducing the operating cost andalso securing a. greater over-all powereiiiciency. Investigation has shown also'thatthe over-all powerefi'iciency is furtlier'increased as a result of i the balancedarrangement of, themodulatoramplifier tubes as shown.

' Because of the balanced arrangement of the tubes VT and VT.,, thevoltage variations to which the grids of these tubes are subj ected mayreadily be held within limits such that the operating point on thecharacteristic curve will not pass beyond the straight portionof saidcurve,fthus avoiding distortion which might otherwise result.

' It is to be understood that modifications Other and furthermodifications of may be made in the above described circuits withoutdeparting from the fundamental principles involved. For instance, aseries of tubes in parallel be substituted for. each of the single tubes"VT, and Vige shown, thus increasing the power output.

, ne circuit may be made within the scope of the appended claimswithoutdepaitin from the a spirit of the invention.

J1. A signal transmission system coinprising a plurality of electrontubes each having grid, filament and plate electrodes, input and outputcircuits interconnecting said electrodes with the input and outputcircuits of one of said :electron tubes mutually coupled for thegeneration of high frequency oscillations, a

signal transmission circuit, and a pair'of balanced circuitsinterconnecting,otlicrsof said electron tubes and interposed betweenSZUCl signal transmission circuit and said high frequency oscillatingcircuit, and a microphone circu tincluding a transformer sysstemhavingjprimaryand secondary windin with thesecondary winding connectedat opposite'ends with grid electrodes of said electron tubes connectedin said balanced CllCllltS for modulating the eilc'ctsfof said high hequency oscillating circuit upon said signal transmission circuit.

2. A signal transmission system comprising a plurality ofelectron tubeseach having grid,

filament and plate electrodes, input and output circuits interconnectingsaid electrodes with the input and output circuits of one of saidelectron tubes mutually coupled for the generation of high frequencyoscillations, a signal transmission circuit, a pair of said electrontubes being connected in balanced relationship with the output circuitsof said trodes of said pair of electron tubes, and connections betweensaid high frequency oscillating circuit and the input circuits of saidpair of electron tubes for impressing high frequency current thereonwhereby the efli'ccts of said currenton said transmission circuit may bevaried in accordance with the operation of saidmicrophone circuit.

3. A signal transmission system comprising a plurality of electron tubeseach having grid,'fila-mentand plate electrodes, input and outputcircuits interconnecting said electrodes, one of said electrontubeshaving iiiductances connected in its input and output circuitsforsustaining high frequency oscillations, a pair of said electron tubesbeing, connected in balanced relationship, a signal transmissioncircuit, connections between the output circuits of said pair ofelectron tubes and said signal transmission circuit, inductances ineachof the input circuitsof said pair of electron tubes, both of saidinductances beingcoupled with the inductances in" the output circuit ofsaid first mentioned tube, a microphone circuit including primaryiandsecondary windings with the secondary winding connected between theinductances in the input circu ts of said pair of electron tubes'wherebythe effects of said high frequency oscillation circuit upon saidtransmis-r S1011 circuit may be variablycontrolled.

LA modulation system comprising in combination a plurality of electrontubes-each having grid, filament and plate electrodes, input and outputcircuit-s intercoiinectingsaid electrodes, connections between the inputcircuits of a pair of said electron tubes, connections between theoutput circuits of said pair ofe'lectron tubes, :1 signal transmissioncircuit, a connection between said last men tion'ed outputcircuits andsaid signal transmissioncircuit, another of said electron tubes havinginput and output circuits mutually 'coupledforthe generation ofoscillations and jfid8p6l1ClO1ltly coupled with the input circuits withthe input circuit of one of said pair of electron tubes, and at theopposite end with 10 the input circuit of the other of the electrontubes of said pair for modulating the effect of said voice controlcircuit on said pair of electron tubes. y c

In testimony whereof I affix my signature.

CHARLES A. CULVER.

